Galleys or kitchen areas in passenger aircraft are equipped with parking spaces for food transport trolleys. It is necessary to store these food stuffs including drinking liquids at sufficiently low temperatures to keep the food stuffs fresh. The transport trolleys have standardized dimensions substantially independent of the aircraft type because such trolleys are used on a worldwide basis and must be suitable for insertion into the above mentioned parking spaces of different aircraft types. These trolleys are filled with food stuffs on the ground and precooled so that they are loaded into the aircraft galley at cooling temperatures. However, these cooling temperatures inside the transport trolleys must be maintained until the food is distributed to the passengers.
Heretofore it has been customary to cool food stuffs on board of an aircraft by various means, for example so-called dry ice, namely carbon dioxide in solid form or cooled air have been used. The cooled air is blown either directly through the transport trolleys or facilities are provided to envelope the transport containers or trolleys by a cool air flow.
The cooling by using dry ice has the disadvantage that it reduces the space available for food stuffs because a special compartment must be provided in the upper section of the transport trolley for holding plates of compressed CO.sub.2 snow. Sublimation generates cold CO.sub.2 gas which falls downwardly to thereby envelope the food stuffs and cool the same. Due to the sublimation the available cooling time is limited and another disadvantage is seen in that the cooling capacity is not controllable, except for the initial selection of the volume of dry ice which is limited by the above mentioned space considerations.
German Patent Publication DE-OS 4,105,034 A1 (Plassmeier et al.) discloses a trolley cooling system in which cooled air is blow into a chamber separated from the space holding the food stuffs in the trolley. Cooling coils or ducts are exposed in the chamber to the flow of the cool air. These cooling coils or ducts are positioned with most of their length in the walls of the transport trolley. The air in the cooled air flow circuit is cooled in turn by a refrigeration unit such as a compression cold vapor machine or air chiller or by a heat exchanger which in turn is cooled at the outer skin of the aircraft body.
The just described air cooling system uses air as a heat carrier, whereby the proper sealing of the air flow circuit is a substantial problem because air leaks are virtually unavoidable. As a result, substantial energy losses are also unavoidable resulting in a low efficiency. Additionally, the available useful space in the transport trolley is reduced by the chamber in which portions of the cooling coils or ducts are exposed to the cool air. Such a reduction of the useful space is a substantial disadvantage, especially in connection with passenger aircraft in which space is at a premium. The reduction of the useful space by the cooling chamber usually results in an increase in the number of total transport trolleys required which in turn increases the packing space for the trolleys and additional trolleys increase the total weight of the aircraft.